The Neurofilament proteins (NFPs) and the glial fibrillary acidic protein (GFAP) are major cytoskeletal elements in the nervous system. Preliminary studies suggest that each NFP is present in filaments isolated from newborn rat brain and spinal cord and that the NFPs are phosphorylated at this stage of development. In the present proposal these studies will be extended. The appearance of the three NFPs will be determined in the rat CNS and PNS during fetal and neonatal life by both the immunoblot technique and immunohistochemistry utilizing monoclonal antibodies. These results will then be correlated with the appearance of morphologically distinct neurofilaments as identified by electron microscopy. Subsequently, phosphorylation of the NFPs in the newborn and fetal rat CNS and PNS will be examined to determine whether these proteins are phosphorylated immediately after their synthesis or only at a later state of neuroaxonal differentiation. The amount of covalently bound phosphate associated with each NFP in the rat CNS will also be analyzed using a developmental approach. The proposed studies on the appearance and phosphorylation of the NFPs during fetal and early postnatal life may provide insight into possible structural, differential or functional roles of the NFPs during nervous system development. Similarly, the in vivo phosphorylation of GFAP will be investigated, initially in the adult rat CNS. Since it has been demonstrated that GFAP is present in rat brain and spinal cord at 14 and 16 days of gestation, respectively, and in rat sciatic nerve at birth, it will be feasible subsquently to ascertain at what stage of development GFAP is first phosphorylated in the CNS and PNS. These developmental studies are designed to examine the role of GFAP phosphorylation in the differentiation of astrocytes and Schwann cells.